One of the primary goals of studies of the motor systems of vertebrates is to understand how the central nervous system controls the activation of motoneurons to generate different motor behaviors. The networks underlying motor behaviors are most easily studied in fish and amphibians because of the smaller number and larger size of their neurons relative to those in mammals. The proposed experiments are designed to examine the spinal circuitry that controls different populations of axial motoneurons during two very different motor behaviors in goldfish - escapes initiated by the Mauthner cell and normal swimming. Intracellular recording and HRP staining techniques will be used to: 1) examine the output connections of identified interneurons in the spinal network of the M-cell. These data will provide essential information about the role of identified interneurons in the network of a well defined vertebrate motor behavior. 2) determine what neurons are polysynaptically activity by the M- cell. These data will permit a detailed comparison between the activation of motoneurons and interneurons by the M-cell network and the swimming network. 3) determine what spinal interneurons and motoneurons are active during fictive swimming in goldfish, as a basis for comparison with both the M-cell network and the spinal network for swimming on other vertebrates. 4) determine directly what synaptic inputs individual interneurons receive from both networks to evaluate the extent to which spinal interneurons are shared by the two. 5) examine interactions between the swimming and M-cell networks by eliciting a M-cell initiated escape during fictive swimming episode. These experiments will provide basic information about the central mechanisms for controlling the activation of axial motoneurons in goldfish. Because previous work indicates broad similarities in the organization of spinal motor systems in vertebrates, the results are likely to provide general insights into mechanisms for control of motoneurons in vertebrates, including humans.